Localized complications are a common occurrence in breast augmentation and breast reconstruction surgery. Among the more serious of these surgical complications are infection, capsular contracture, hematoma and pain. Women who have undergone radiation therapy as part of their breast cancer treatment appear to sustain higher rates of post-surgical infection and capsular contracture.
Infection can occur anytime from several days to several years after implantation; however, it occurs more frequently in the immediate post-operative period. Acute infection is diagnosed when the patient exhibits pain, fever, and tenderness around the implant between several days and six weeks from the time of surgery. According to one report, the incidence of infection ranges from 1-24% (Nahabedian et al. (2003) Plast. Reconstr. Surg. 112:467-76) with Staphylococcus aureus, Propionii acne and Staphylococcus epidermis among the cultured bacteria from colonized implants (Pittet et al (2005) Lancet Infect. Dis. 5:94-106).
Another issue arising with the use of breast implants is the formation of excess scar tissue around an implant. Such tissue can harden and lead to tightening around or squeezing of the implant, a phenomenon known as capsular contracture. While scar tissue and capsule formation is a normal process, when capsular contracture occurs the breast can become misshapen, painful, hard and attain an unnatural appearance and feel. Additionally, capsular contracture appears to be more common following infection, hematoma and seroma. Textured implant surfaces and submuscular placement of the implant may decrease the rate of capsular contracture (FDA Breast Implant Consumer Handbook, 2004, p. 28).
Implant infection is most commonly attributed to contamination of the sterile field during surgery or to contamination arising from lymph node or mammary duct dissection during surgery. Bacteria can migrate deep within the breast tissue via the mammary ducts. Incision through the ducts during subglandular placement thus opens a temporary but direct external route for contamination of the implant after placement. Bacteria colonized from the mammary ducts and nipples is similar to exogenous flora found on the skin, namely coagulase negative Staphylococcus, P. acne, and Bacillus subtillus (Pittet, supra).
Subclinical infection is perceived to be the a contributor to capsular contracture. Subclinical infection is defined as bacterial colonization of a surface with or without biofilm formation. It does not produce the signs and symptoms traditionally associated with frank infection (such as pain, tenderness, fever, and pus) and manifests itself as a chronic inflammatory response. This inflammatory response can produce constant tissue remodeling that leads to fibrous tissue buildup and eventual implant distortion and capsule rigidity.
Most surgeons engage in prophylactic efforts to reduce the incidence of infection associated with breast implants. For example, in addition to meticulous attention to sterility, many surgeons irrigate the implant pocket with betadine, gentamycin, cefazolin, povidone-iodine or another antibiotic solution. Post-operative counseling measures include instructing the patient to neither touch the incision sites nor to immerse them in hot water for at least two weeks (or until healing is complete). Prophylactic oral antibiotics can also given to patients prior to surgery to prevent post-implant colonization. Additionally, implant placement below the muscle avoids (or at least minimizes) surgical contact with the mammary ducts.
Adams and colleagues devised a method for reducing capsular contracture caused by bacterial implant colonization. They optimized the antibacterial irrigation solution and employed sterile technique prior to and during surgery. Adams' “triple antibiotic solution” originally contained a mixture of bacitracin, gentamycin, and cefazolin and was shown to be active against bacteria most commonly known to colonize breast implants. Adams subsequently published results of a six-year clinical study showing that patients who received surgeries incorporating these techniques have a 1% capsular contracture rate as opposed to national rates, which approached 15-20% in that same time period (Adams et al. (2006) Plast. Reconstr. Surg. 117:30-36).
To increase the length of time during which an antibiotic or antimicrobial agent resides within the vicinity of the breast implant, Darouiche and colleagues soaked silicone breast implants with a combination of rifampin and minocycline and implanted them in a rabbit model. While the antibiotic-soaked implants prevented bacterial colonization relative to unsoaked control implants, the soaking process caused the antibiotics to leach into the silicone gel as evidenced by implant swelling. In another instance, surgeons injected povidone-iodine solution directly into the breast implant but this entails a risk because the silicone shell can weaken and leak. In fact, the FDA has stated that povidone-iodine is contraindicated for use with breast implants as a result of reported ruptures with its use.
Some of the efforts to reduce capsular contracture involve post-operative measures, including counseling the patient to massage the implant (after the initial healing period is complete) and taking vitamin E. Once capsular contracture has occurred, anecdotal evidence indicates that orally-administered leukotriene receptor antagonists can reduce the amount of capsular contracture (U.S. Pat. No. 6,951,869 to Schlesinger).
Texturing the outside silicone surface has been employed as a technique to prevent capsular contracture. The textured surface is believed to be more biocompatible and to promote tissue ingrowth. However, these implants have not significantly penetrated the market because, in use, the implants may become firmly placed under the skin, which often leads to a visible dimpling effect when the recipient moves. Textured implants also tend to have thicker shells than smooth implants and higher rupture rates.
Quaid describes a method in which a biocompatible, non-bioabsorbable uncured silicone elastomer is applied to the outer surface of a silicone implant to create an outer layer (U.S. Pat. No. 4,889,744). Solute particles, usually salt, are embedded in the tacky layer which is then partially cured, exposed to an appropriate solvent to remove the solute particles, and then fully cured. The plurality of voids remaining in the layer following removal of solute from the fully-cured, outer layer leaves an open celled structure. The resulting medical implant has both a textured outer surface and unitary construction. McGhan describes hybrid implants made with a biocompatible, bioabsorbable material adhered to the typically silicone shell of the implant (U.S. Pat. No. 6,913,626. In one embodiment, McGhan's implants have discrete bioabsorbable particles partially embedded in the outer shell.
Brauman describes breast implants with a layer laminated or bonded (e.g., glued) to the implant shell (U.S. Pat. No. 4,648,880 and RE35,391). The layer has a rough textured surface and is made from non-biodegradable material such as Dacron® (poly(ethylene glycol terephthalate)), Teflon® or silicone. Brauman's implants may optionally contain a barrier layer bonded between the shell and the outer layer. Such implants are susceptible to delaminating within the body.
The partial or total adhesion of the implant to the capsule due to such tissue ingrowth may be undesirable in the event it becomes necessary to remove or replace the implant. Further, partial or asymmetric adhesion between the capsule and the outer surface of the implant may give rise to undesirable cosmetic effects. Notwithstanding the foregoing disadvantages, textured implants having a biocompatible, non-bioabsorbable outer tissue-contacting surface are generally considered to reduce the incidence of capsular contracture in patients. Nevertheless, there remains a need for an implantable fluid-filled prosthesis that resists capsular contracture following implantation and that resists adherence of the implant to the capsule.
The biodegradable coverings of the present invention overcome these drawbacks while reducing or preventing capsular contracture as well as treating or preventing infection, pain, inflammation, scarring or other complications associated with breast augmentation or breast reconstruction.